1. Field of the Invention
The present invention relates to a multi charged particle beam writing apparatus and a multi charged particle beam writing method. For example, the present invention relates to a method of obtaining the high accuracy of multi-beam writing.
2. Description of Related Art
The lithography technique that advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a wafer, etc. with electron beams.
As an example using the electron beam writing technique, there is a writing apparatus using multiple beams (multi-beams). Since it is possible for a multi-beam writing apparatus to perform irradiation with many beams at a time, throughput can be greatly increased compared with the case of writing using one electron beam. In such a writing apparatus of a multi-beam system, for example, multiple beams are formed by letting an electron beam emitted from the electron gun assembly pass through a mask with a plurality of holes arranged in a matrix, blanking control is performed for each beam, and each of unblocked beams is deflected by a deflector so as to irradiate a desired position on a target object or “sample” (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2006-261342).
In such a writing apparatus of the multi-beam system, irradiation of a plurality of beams is performed at a time, and a pattern is written by combining “beam on” and “beam off” by blanking control as described above. Regarding the writing apparatus of the multi-beam system, there is a concern about yield (generation of a defective beam) because of structural complexity for forming and controlling a plurality of beams. For example, a defective beam being continuously “beam off” may be generated when “beam on” control cannot be performed. In addition, there is a case where a defective beam is generated because it is impossible to obtain a specified amount of beam current even if “beam on” control can be performed or impossible to control a dose to have a desired accuracy because of poor responsiveness even when “beam on” control and “beam off” control are performed for a predetermined irradiation time. When a defective beam of this kind exists, a problem occurs in that a desired pattern is not written or desired writing accuracy is not obtained even when writing is performed.
For example, there is thought of a method of maintaining writing accuracy by redundancy, that is, preparing many more beams against generation of a defective beam in order to respond by using other beam instead of the defective beam. This method is, for example, that if a position on a target object is irradiated with one-hundred beams, even when one of the beams is defective, the dose will have 1% error at most. However, with recent miniaturization of patterns, approximately 0.1% of accuracy, for example, is required for the dose accuracy. Thus, for maintaining the accuracy of 0.1% by using the redundancy, theoretically, beams of 1000 times the number of beams to be used for writing are needed. As a result, in order to maintain the writing accuracy by using the redundancy, it is necessary to newly prepare hardware resource and software resource for a huge number of beams being 1000 times the number of beams used in the case of no redundancy, thereby requiring excessive structure for the apparatus. Therefore, it is desired to solve the problem of defective beams by a different method from the method of increasing the number of beams.